Eucalyptus organosolv lignins: study of the hydroxymethylation and use in resols

Lignins obtained from Acetosolv and Formacell delignification of Eucalyptus grandis chips (EAc and EFo, respectively) were reacted with formaldehyde i n alkaline medium. The hydroxymethylation was followed by dynamic DSC, to d etermine the relative reactivity of both lignins. TGA results showed that h ydroxymethylated lignins are thermally stable up to 250 degrees C, while th e original lignins are stable until 200 degrees C. The synthesis of resols containing EAc and EFo lignins were carried out following multivariate fact orial designs (2(4-1)). The effects of four parameters were studied on the synthesis time and on the final viscosity (eta). The NaOH:phenolics ratio a nd the solid content have the more significant effects on the synthesis tim e and eta, for both lignins. Shorter synthesis time is obtained increasing the lignin:phenol ratio from 2:3 to 1:1 for EAc and EFo lignin, but the eff ect of the HCHO:phenolics ratio is important only for resols containing EFo . For this study, the multivariate experimental design is more adequate tha n an univariate method, since there is a large interaction between the synt hesis parameters as demonstrated by the second order effects. (C) 1998 Publ ished by Elsevier Science Ltd. All rights reserved.